(1) Field of the Invention
The present invention generally relates to a scanning radar apparatus, and more particularly to a scanning radar apparatus of an automotive vehicle which detects a direction of a center of a target, such as an advancing vehicle, by receiving reflection beams from the target.
(2) Description of the Related Art
In recent years, several types of radar devices for use in automotive vehicle have been developed in order to provide increased stability and operability of the automotive vehicle. The radar devices are capable of detecting a relative distance between a target (such as an advancing vehicle) and the vehicle, and a relative velocity of the target to a vehicle speed of the vehicle.
Japanese Laid-Open Patent Application No. 4-158293 teaches a radar apparatus which is one of the above-mentioned types. The radar apparatus utilizes a radar unit radiating a laser beam in order to detect a target such as an advancing vehicle in a forward direction of the radar apparatus.
To make use of the radar apparatus of the above publication, reflectors are mounted at a right-side rear end and a left-side rear end of the advancing vehicle. The radar apparatus receives reflection laser beams reflected off the reflectors of the advancing vehicle (the target). The radar apparatus detects a distance of each of the reflectors by measuring the time for the radiation laser beam to return to the radar apparatus after it has been reflected off the advancing vehicle. When the distances of the reflectors are detected to be the same, the radar apparatus determines a center scanning angle of the radar unit for a center of the advancing vehicle by detecting a mid-point between two scanning angles for the reflectors.
Another type is a radar apparatus utilizing a radar unit radiating an extremely high frequency (EHF) electromagnetic wave in order to detect the target. However, in a case of the radar apparatus of this type, the radar apparatus receive reflection radar beams containing noises from the reflectors of the advancing vehicle, and the reflection of the radiation radar beam on the advancing vehicle is not uniform.
It is difficult for the above-mentioned radar apparatus to accurately detect a position of an end of the advancing vehicle by measuring the time for the radiation radar beam to return to the radar apparatus after it has been reflected off the advancing vehicle. It is practically impossible for the above-mentioned radar apparatus to determine a center scanning angle of the radar unit for a center of the advancing vehicle by detecting a mid-point between two scanning angles for the reflectors as in the laser-beam radar apparatus.
Therefore, when the conventional radar apparatus utilizing the radar unit radiating the EHF electromagnetic wave is used, it is difficult to accurately detect the direction of the center of the target.
An object of the present invention is to provide an improved radar apparatus in which the above-described problems are eliminated.
Another object of the present invention is to provide a radar apparatus of an automotive vehicle which accurately detects a direction of a center of a target in a forward direction of the vehicle by performing a similarity approximation using an antenna directional gain pattern of a radar unit.
Still another object of the present invention is to provide a radar apparatus of an automotive vehicle which accurately detects individual targets in a forward direction of the vehicle by separately processing the data of received reflection signals related to one target from the data related to another when a plurality of adjacent targets are running in parallel in the forward direction of the vehicle.
A further object of the present invention is to provide a radar apparatus of an automotive vehicle which easily and accurately detects individual targets in a forward direction of the vehicle by separately performing a pairing of the data of received reflection signals related to one target and a pairing of the data of received reflection signals related to another target when a plurality of targets in the forward direction of the vehicle are detected.
The above-mentioned objects of the present invention are achieved by a radar apparatus which includes: a radar unit which radiates an electromagnetic wave to a target in a forward direction of the vehicle and receives reflection beams from the target to detect the target; a scanning control unit which performs a beam scanning of the radar unit to the target so that the reflection beams during the beam scanning are received; and a center direction determining unit which detects a distribution pattern of the received reflection beams with respect to respective scanning angles of the radar unit, performs a similarity approximation of the distribution pattern by using an antenna directional gain pattern of the radar unit to produce an approximated distribution pattern, and determines a direction of a center of the target based on a peak of the approximated distribution pattern.
The radar apparatus of the present invention can determine a direction of a center of the target by performing the similarity approximation even when the reflection of the radiation beam on the target is not uniform and noises are superimposed in the received reflection beams. Accordingly, it is possible for the radar apparatus of the present invention to accurately detect the direction of the center of the target for a center scanning angle of the radar unit.